Vehicle seat device

ABSTRACT

A vehicle seat device includes a seat cushion disposed on a floor of a vehicle, a seat back linked to a rear end part of the seat cushion, and a headrest fitted to an upper end part of the seat back, wherein a vibration system that also includes the seat back and the headrest is equipped with a dynamic damper. The dynamic damper includes an elastic member that is embedded within a cushion member of the vibration system, and a weight embedded in the elastic member. The weight has a center of gravity thereof set to a position offset to at least one side from a center of the cushion member in an up-and-down direction of a seat, and the weight has an asymmetric shape in at least one of a lateral direction and an up-and-down direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/345,450, filed Mar. 18, 2014, which is the US National Phase ofPCT/JP2012/074344 filed Sep. 24, 2012, which claims priority under 35USC § 119 based on Japanese patent application No. 2011-208309, filed onSep. 25, 2011. The subject matter of these priority documents areincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an improvement of a vehicle seat devicethat includes a seat cushion disposed on a floor of a vehicle, a seatback linked to a rear end part of the seat cushion, and a headrestfitted to an upper end part of the seat back, the seat provided with avibration system that includes the seat back and the headrest beingequipped with a dynamic damper.

BACKGROUND ART

The dynamic damper in such a vehicle seat device exhibits a dampingaction of suppressing vibration in the fore-and-aft direction and/or inthe left-and-right direction of the seat back and headrest while thevehicle is traveling, and such a vehicle seat device is known, asdisclosed in Japanese Patent Application Laid-open No. 10-226255.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Conventionally, in such a vehicle seat device, since the dynamic damperis formed from a plurality of coil springs, a bracket, a weight held bythe bracket, and retaining means that connects the coil springs to aframe of the vibration system and the bracket, the number of componentsis large and the structure is complicated.

The present invention has been accomplished in light of suchcircumstances, and it is an object thereof to provide a vehicle seatdevice that includes a dynamic damper having a small number ofcomponents and a simple structure.

Means for Solving the Problems

In order to attain the above object, according to a first aspect of thepresent invention, there is provided a vehicle seat device comprising aseat cushion disposed on a floor of a vehicle, a seat back linked to arear end part of the seat cushion, and a headrest fitted to an upper endpart of the seat back, a vibration system comprising the seat back andthe headrest being equipped with a dynamic damper, characterized in thatthe dynamic damper comprises an elastic member that is embedded orwrapped around within a cushion member of the vibration system and isformed from a rubber or elastomer that is softer than the cushionmember, and a weight embedded or wrapped around in the elastic member.It should be noted here that the frame of the vibration systemcorresponds to a seat back frame 10 and a headrest frame 12 of anembodiment of the present invention, which is described later, and thecushion member of the vibration system corresponds to a cushion member38 of a seat back 3 and a cushion member 13 of a headrest 4.

Further, according to a second aspect of the present invention, inaddition to the first aspect, the dynamic damper is disposed so thatpart of the cushion member is present between the elastic member and aframe of the vibration system.

Furthermore, according to a third aspect of the present invention, inaddition to the second aspect, the dynamic damper is embedded in thecushion member of the headrest so that the center of gravity of theweight of the dynamic damper is present above a center in an up-and-downdirection of the headrest.

Moreover, according to a fourth aspect of the present invention, inaddition to any one of the first to third aspects, the headrestcomprises a headrest frame that is supported on a support tube so thatthe headrest frame can move up and down and be fixed, the support tubebeing fixedly provided on an upper end part of a seat back frame of theseat back, and the cushion member that is supported on the headrestframe, and the dynamic damper is embedded in the cushion member so thatwhen viewed from a side the weight is present on an extension axis ofthe support tube.

Further, according to a fifth aspect of the present invention, inaddition to any one of the first to fourth aspects, the headrestcomprises a headrest frame and the cushion member, the headrest frame isformed from a frame lower portion supported on the support tube so thatthe frame lower portion can move up and down and be fixed, the supporttube being fixedly provided on an upper end part of a seat back frame ofthe seat back, and a frame upper portion bending forward from an upperend of the frame lower portion and extending obliquely upward, thecushion member is supported on the frame upper portion, and the dynamicdamper is embedded in the cushion member so as to be positioned to therear of the frame upper portion.

Furthermore, according to a sixth aspect of the present invention, inaddition to the first or second aspect, the dynamic damper is embeddedas a pair in left and right shoulder parts of the cushion member of theseat back.

Moreover, according to a seventh aspect of the present invention, inaddition to any one of the first to sixth aspects, the weight of thedynamic damper is formed so that an upper half portion of the weight hasa mass that is larger than a mass of a lower half portion.

Further, according to an eighth aspect of the present invention, inaddition to any one of the first to seventh aspects, the elastic memberof the dynamic damper is formed so that a spring constant thereof variesbetween that when the weight vibrates in a fore-and-aft direction of thevehicle and that when the weight vibrates in a left-and-right directionof the vehicle.

Furthermore, according to a ninth aspect of the present invention, thereis provided a vehicle seat device comprising a seat cushion disposed ona floor of a vehicle, a seat back linked to a rear end part of the seatcushion, and a headrest fitted to an upper end part of the seat back, avibration system comprising the seat back and the headrest beingequipped with a dynamic damper, characterized in that the dynamic dampercomprises an elastic member that is supported on a headrest frame of theheadrest so as to wrap around the headrest frame and is formed from arubber or elastomer that is softer than a cushion member of the seatback, and a weight embedded or wrapped around in the elastic member.

Effects of the Invention

In accordance with the first aspect of the present invention, since thedynamic damper is formed from the elastic member that is embedded orwrapped around within the cushion member of the vibration system and isformed from a rubber or an elastomer that is softer than the cushionmember, and the weight embedded or wrapped around in this elasticmember, simply embedding or wrapping the elastic member having theweight embedded or wrapped around therein within the cushion member ofthe vibration system enables the dynamic damper to be easily mounted onthe vibration system, that is, the headrest or the seat back, it istherefore unnecessary to use a plurality of coil springs, springretaining means, a bracket for holding a weight, etc. as isconventional, and a vehicle seat device equipped with a dynamic damperhaving a small number of components and a simple structure can beprovided at low cost.

In accordance with the second aspect of the present invention, since thedynamic damper is disposed so that part of the cushion member of thevibration system is present between the elastic member of the dynamicdamper and the frame of the vibration system, it is possible to preventthe elastic member from coming into contact with the frame of thevibration system, thus making the dynamic damper exhibit a good dampingfunction.

In accordance with the third aspect of the present invention, since thedynamic damper is embedded in the cushion member of the headrest so thatthe center of gravity of the weight is present above the center in thevertical direction of the headrest, the center of gravity of the weightis present at a position that is in effect the furthest from the part ofthe vibration system that is supported on the seat cushion, thereforemaking it possible to impart to the dynamic damper a predetermineddamping function by means of a weight having a relatively small mass andthereby contributing to lightening the weight of the vehicle seatdevice.

In accordance with the fourth aspect of the present invention, since thedynamic damper is disposed so that when viewed from the side the weightthereof is present on the extension axis of the support tube of the seatback frame, which supports the headrest frame so that it can move up anddown and be fixed, it is possible for the damping action of the dynamicdamper to be exerted on the seat back frame efficiently, thus dampingthe vibration system effectively.

In accordance with the fifth aspect of the present invention, since thedynamic damper is disposed to the rear of the frame upper portion, whichextends upward while bending forward from the upper end of the framelower portion of the headrest frame, it is possible to efficientlydispose the headrest frame and the dynamic damper in a thickness rangethat is limited in the fore-and-aft direction of the cushion member ofthe headrest, thereby avoiding an increase in size of the headrest.

In accordance with the sixth aspect of the present invention, the pairof dynamic dampers embedded in the left and right shoulder parts of thecushion member of the seat back enable vibration of the vibration systemthat includes the seat back and the headrest to be suppressed. Moreover,since the dynamic dampers, which are divided into a pair, areindividually compact, they can be embedded compactly in the two shoulderparts of the seat back so as not to affect the comfort of a seateddriver.

In accordance with the seventh aspect of the present invention, thecenter of gravity of the weight is present at a position above thecenter in the vertical direction of the weight, and the center ofgravity of the weight is accordingly further away than the part of thevibration system that is supported on the seat cushion, therefore makingit possible to impart to the dynamic damper a predetermined dampingfunction by means of a weight having a relatively small mass and therebycontributing to lightening the weight of the vehicle seat device.

In accordance with the eighth aspect of the present invention, when thenatural frequency of the dynamic damper varies between that when it isvibrated in the left-and-right direction and that when it is vibrated inthe fore-and-aft direction, making the vibration direction and naturalfrequency correspond to the direction and frequency of vibrationtransmitted from the floor to the vibration system via the seat cushionenables the vibration system to be damped effectively.

In accordance with the ninth aspect of the present invention, vibrationof the vibration system that includes the seat back and the headrest canbe suppressed by means of resonance vibration of the weight accompaniedby elastic vibration of the elastic member. Moreover, the elastic memberof the dynamic damper also functions as a cushion member of theheadrest, the number of components can be cut accordingly, and thestructure can be simplified.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a vehicle seat device related to a firstembodiment of the present invention. (first embodiment)

FIG. 2 is an enlarged view of part 2 in FIG. 1. (first embodiment)

FIG. 3 is a sectional view along line 3-3 in FIG. 2. (first embodiment)

FIG. 4 is a diagram for explaining a method of producing a headrestequipped with a dynamic damper. (first embodiment)

FIG. 5 is a view, corresponding to FIG. 2, of a second embodiment of thepresent invention. (second embodiment)

FIG. 6 is a sectional view along line 6-6 in FIG. 5. (second embodiment)

FIG. 7 is a view, corresponding to FIG. 2, of a third embodiment of thepresent invention. (third embodiment)

FIG. 8 is a sectional view along line 8-8 in FIG. 7. (third embodiment)

FIG. 9 is a front view of a part of a vehicle seat device showing afourth embodiment of the present invention. (fourth embodiment)

FIG. 10 is a view, corresponding to FIG. 2, of a fifth embodiment of thepresent invention. (fifth embodiment)

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

-   -   2 Seat cushion    -   3 Seat back    -   4 Headrest    -   6 Seat cushion frame    -   10 Seat back frame    -   11 Support tube    -   12 Headrest frame    -   13 Cushion member of headrest    -   15 a Frame lower portion    -   15 b Frame upper portion    -   18 Vibration system    -   20 Dynamic damper    -   21 Elastic member    -   22 Weight    -   38 Cushion member of seat back    -   F Floor    -   G Center of gravity of weight    -   S1 Center in vertical direction of weight    -   Y Extension axis of support tube

MODES FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention shown in FIG. 1 to FIG. 4 isnow explained.

First Embodiment

In FIG. 1, a seat 1 for a vehicle is formed from a seat cushion 2, aseat back 3, and a headrest 4. The seat cushion 2 has a seat cushionframe 6 having a plurality of support legs 7 and 7 formed in its lowerpart, and the support legs 7 and 7 are secured to a floor F of thevehicle.

A left and right pair of brackets 8 protruding upward are provided so asto be connected to a rear end part of the seat cushion frame 6, and aseat back frame 10 of the seat back 3 is linked to these brackets 8 viaa pivot shaft 9 in a reclinable manner.

Furthermore, a pair of left and right support tubes 11 and 11 arefixedly provided on an upper end part of the seat back frame 10, andthese support tubes 11 and 11 support the headrest 4 so that it can moveup and down and be fixed.

As shown in FIG. 2 and FIG. 3, the headrest 4 is formed from a headrestframe 12, a cushion member 13 that is made of a urethane foam and issupported on the headrest frame 12, and a skin 14 covering the surfaceof the cushion member 13.

The headrest frame 12 is formed from a pair of left and right rod parts15 and 15 supported by the pair of support tubes 11 and 11, and alinking part 16 integrally linking upper ends of these rod parts 15 and15, and has a gate shape when viewed from the front. Furthermore, theleft and right rod parts 15 and 15 are formed from a frame lower portion15 a supported by the support tubes 11 and 11 and extending upward and aframe upper portion 15 b extending upward to the linking part 16 whilebending forward from the upper end of the frame lower portion 15 a, theframe upper portion 15 b and the linking part 16 being embedded in thecushion member 13 to thus support the cushion member 13.

Thus, the seat back 3 and the headrest 4 form a continuous vibrationsystem 18 linked to the seat cushion frame 6 via the pivot shaft 9, andin order to suppress vibration of the vibration system 18 a dynamicdamper 20 is provided within the headrest 4.

The dynamic damper 20 is formed from an elastic member 21, which isembedded in the cushion member 13 of the headrest 4, and a weight 22embedded in the elastic member 21, the elastic member 21 being made of arubber or elastomer that is softer than the cushion member 13, and theweight 22 being made of a metal.

When this dynamic damper 20 is embedded in the cushion member 13, thedynamic damper 20 is disposed to the rear of the frame upper portion 15b.

Furthermore, the dynamic damper 20 is disposed so that part of thecushion member 13 is present between the elastic member 21 and theheadrest frame 12.

Moreover, the dynamic damper 20 is disposed so that the center ofgravity G of the weight 22 is above a center S1 in the verticaldirection of the headrest 4.

Furthermore, the dynamic damper 20 is disposed so that when viewed fromthe side the weight 22 thereof is present on an extension axis Y of thesupport tube 11.

Moreover, the dynamic damper 20 is disposed so that part thereofprotrudes upward from the upper end of the headrest frame 12.

A method of embedding the dynamic damper 20 in the headrest 4 isexplained by reference to FIG. 4.

Attached to a lower face of a machine platform 25 are molding dies 27 aand 27 b, which form a cavity 26 corresponding to the external shape ofthe headrest 4 excluding the headrest frame 12 and can be opened andclosed in the vertical direction, and provided in advance on an innerface of the cavity 26 so as to be stretched over it is the skin 14 ofthe headrest 4. Furthermore, a support plate 29 having a foam materialinjection opening 28 that opens in the cavity 26 is fixed to an upperface of the molding platform 25, and a foam material supply device 30having its nozzle 30 a facing the foam material injection opening 28 ismounted on the support plate 29. Moreover, the headrest frame 12, whichis disposed within the cavity 26 through the foam material injectionopening 28, is supported by a bracket 37 provided on the support plate29. Furthermore, the dynamic damper 20 is connected to a thread 32retained on a hook 31 on the support plate 29, and the dynamic damper 20is suspended at a predetermined position within the cavity 26 throughthe foam material injection opening 28. In this case, the weight 22 ofthe dynamic damper 20 is made of iron, and a magnet 33 for imparting tothe weight 22 an attractive force so as to stabilize the dynamic damper20 at the predetermined position is attached to the lower molding die 27b. The molding dies 27 a and 27 b are made of a non-magnetic syntheticresin so that they do not interfere with the magnetic action of themagnet 33 on the weight 22.

Thus, a foam material 34 such as a urethane is injected into theinterior of the skin 14, which is bag shaped and in intimate contactwith the inner face of the cavity 26, through the nozzle 30 a of thefoam material supply device 30 and is made to foam, thus forming thecushion member 13 that wraps around the headrest frame 12 and thedynamic damper 20 within the skin 14. The headrest 4 thus produced canbe taken out from the dies by opening the molding dies 27 a and 27 b inthe vertical direction.

The operation of the first embodiment is now explained.

While the vehicle is traveling, in the dynamic damper 20, the weight 22undergoes resonant vibration accompanied by elastic vibration of theelastic member 21 to thus provide alternative absorption of thevibrational energy of the vibration system 18, when it is transmitted tothe vibration system 18 from the floor F of the vehicle via the seatcushion 2 and the pivot shaft 9, and it is thus possible to damp thevibration system 18, that is, the seat back 3 and the headrest 4.

Moreover, since the dynamic damper 20 is formed from the elastic member21, which is embedded within the cushion member 13 of the headrest 4 andmade of a rubber material that is softer than the cushion member 13, andthe weight 22, which is embedded in the elastic member 21, simplyembedding the elastic member 21 having the weight 22 embedded thereinwithin the cushion member 13 enables the dynamic damper 20 to be mountedeasily on the headrest 4. That is, it is unnecessary to use a pluralityof coil springs, spring retaining means, a bracket for holding a weight,etc. as is conventional, and a vehicle seat device equipped with thedynamic damper 20 having a small number of components and a simplestructure can be provided at low cost.

Furthermore, since the dynamic damper 20 is disposed to the rear of theframe upper portion 15 b, which extends upward while bending forwardfrom the upper end of the frame lower portion 15 a of the headrest frame12, it is possible to efficiently dispose the headrest frame 12 and thedynamic damper 20 in a thickness range that is limited in thefore-and-aft direction of the cushion member 13 of the headrest 4,thereby avoiding an increase in size of the headrest 4.

Furthermore, since the dynamic damper 20 is disposed so that part of thecushion member 13 is present between the elastic member 21 of thedynamic damper 20 and the headrest frame 12, it is possible to preventthe elastic member 21 from coming into contact with the headrest frame12, thus making the dynamic damper 20 exhibit a good damping function.

Moreover, since the dynamic damper 20 is disposed so that the center ofgravity G of the weight 22 is present above the center S1 in thevertical direction of the headrest 4, the center of gravity G of theweight 22 is present at a position that is in effect the furthest fromthe point of the vibration system supported on the seat cushion 2,therefore making it possible to impart to the dynamic damper 20 adamping function by means of the weight 22 having a relatively smallmass and thereby contributing to lightening the weight of the vehicleseat device.

Furthermore, since the dynamic damper 20 is disposed so that when viewedfrom the side the weight 22 thereof is present on the extension axis Yof the support tube 11 of the seat back frame 10, which supports theheadrest frame 12 so that it can move up and down and be fixed, it ispossible for the damping action of the dynamic damper 20 to be exertedon the seat back frame 10 efficiently, thus damping the vibration system18 effectively.

A second embodiment of the present invention shown in FIG. 5 and FIG. 6is now explained.

Second Embodiment

In this second embodiment, a weight 22 of a dynamic damper 20 is formedso that the mass of its upper half portion is larger than the mass ofits lower half portion. Specifically, the weight 22 is formed in areverse trapezoidal shape when viewed from the side. By so doing, thecenter of gravity G of the weight 22 is present at a position above acenter S2 in the vertical direction of the weight 22, and the center ofgravity G of the weight 22 is correspondingly further away from the partof the vibration system that is supported on a seat cushion 2, thereforemaking it possible to impart to the dynamic damper 20 a damping functionby means of the weight 22 having a relatively small mass and therebycontributing to lightening the weight of the vehicle seat device.

Furthermore, an elastic member 21, which houses the weight 22 in itsinterior, is formed so that its spring constant when receiving a load inthe left-and-right direction from the weight 22 is different from itsspring constant when receiving a load in the fore-and-aft direction. Byso doing, when the natural frequency of the dynamic damper 20 variesbetween that when it is vibrated in the left-and-right direction andthat when it is vibrated in the fore-and-aft direction, making thevibration direction and natural frequency correspond to the directionand frequency of vibration transmitted from a floor F to a vibrationsystem 18 via the seat cushion 2 enables the vibration system 18 to bedamped effectively.

In order to make the spring constant of the elastic member 21 whenreceiving a load in the left-and-right direction from the weight 22 bedifferent from a spring constant when receiving a load in thefore-and-aft direction, in the illustrated example the elastic member 21is formed so as to have a thickness T1 in the left-and-right directionand a thickness T2 in the fore-and-aft direction that are different fromeach other. For example, it is formed so that the thickness T1 in theleft-and-right direction is larger than the thickness T2 in thefore-and-aft direction. Changing the thickness of the elastic member 21in this way so as to impart directionality to the spring constant asdescribed above is effective in simplifying the structure.

Furthermore, the same effect may be obtained by forming a portion of theelastic member 21 that receives a load in the left-and-right directionfrom the weight 22 and a portion that receives a load in thefore-and-aft direction from the weight 22 from rubber materials havingdifferent Young's moduli.

The arrangement is otherwise the same as that of the first embodiment;parts in FIG. 5 and FIG. 6 corresponding to those in the firstembodiment are denoted by the same reference numerals and symbols, andduplication of the explanation is omitted.

A third embodiment of the present invention shown in FIG. 7 and FIG. 8is now explained.

Third Embodiment

In this third embodiment, a linking part 16 on an upper end part of aheadrest frame 12 is formed so as to have a recess 36 in its centralpart, whereas a dynamic damper 20 is disposed so that part thereofenters the recess 36. The arrangement is otherwise the same as that ofthe first embodiment; parts in FIG. 7 and FIG. 8 corresponding to thosein the first embodiment are denoted by the same reference numerals andsymbols, and duplication of the explanation is omitted.

In accordance with this third embodiment, it becomes possible to placethe dynamic damper 20 sufficiently close to the linking part 16 in theupper end part of the headrest frame 12, and it is possible toefficiently dispose the headrest frame 12 and the dynamic damper 20 in athickness range that is limited in the fore-and-aft direction of thecushion member 13 of the headrest 4, thereby achieving a small size forthe headrest 4.

A fourth embodiment of the present invention shown in FIG. 9 is nowexplained.

Fourth Embodiment

In this fourth embodiment, in a seat back 3, a pair of dynamic dampers20 are embedded in left and right shoulder parts of a cushion member 13supported by a seat back frame 10, and each dynamic damper 20 is formed,in the same manner as in the first embodiment, from an elastic member 21and a weight 22 embedded therein. The arrangement is otherwise the sameas that of the first embodiment; parts in FIG. 9 corresponding to thosein the first embodiment are denoted by the same reference numerals andsymbols, and duplication of the explanation is omitted.

In accordance with this fourth embodiment, the pair of dynamic dampers20 and 20 embedded in the left and right shoulder parts of the cushionmember 13 of the seat back 3 enable vibration of a vibration system 18comprising the seat back 3 and a headrest 4 to be suppressed. Moreover,since the dynamic dampers 20 and 20, which are divided into a pair, areindividually compact, they can be embedded compactly in the two shoulderparts of the seat back 3 so as not to affect the comfort of a seateddriver.

Finally, a fifth embodiment of the present invention shown in FIG. 10 isexplained.

Fifth Embodiment

In this fifth embodiment, a dynamic damper 20 is formed from an elasticmember 21 supported on a headrest frame 12 of a headrest 4 so as to wraparound it, and a weight 22 embedded in the elastic member 21. Theelastic member 21 is made of a rubber or elastomer that is softer than acushion member 38 of a seat back 3, and also functions as a cushionmember of the headrest 4.

The arrangement is otherwise the same as that of the first embodiment;parts in FIG. 10 corresponding to those in the first embodiment aredenoted by the same reference numerals and symbols, and duplication ofthe explanation is omitted.

In accordance with this fifth embodiment also, vibration of a vibrationsystem 18, which includes the seat back 3 and the headrest 4, can besuppressed by means of resonance vibration of the weight 22 accompaniedby elastic vibration of the elastic member 21. In this arrangement,since elastic vibration of the elastic member 21, which also functionsas the cushion member of the headrest 4, occurs in part of an areaaround the weight 22, almost no vibration occurs on an outer surfaceportion with which a driver's head is in contact. Moreover, since theelastic member 21 of the dynamic damper 20 also functions as a cushionmember of the headrest 4, the number of components can be cutaccordingly, and the structure can be simplified.

The present invention is not limited to the above embodiments and may bemodified in a variety of ways as long as the modifications do not departfrom the spirit and scope thereof.

The invention claimed is:
 1. A vehicle seat device comprising a seatcushion disposed on a floor of a vehicle, a seat back linked to a rearend part of the seat cushion, and a headrest fitted to an upper end partof the seat back, the seat back and the headrest cooperating to form avibration system equipped with a dynamic damper, wherein: the dynamicdamper comprises an elastic member that is embedded within a cushionmember of the vibration system, and a weight embedded in the elasticmember, the weight has a center of gravity which is offset upwardly ordownwardly from a center of the cushion member, the weight has anasymmetric shape in at least one of a lateral direction and anup-and-down direction, and the headrest comprises a headrest frame thatis supported on a support tube so that the headrest frame can move upand down and be fixed, the support tube being fixedly provided on anupper end part of a seat back frame of the seat back, and the cushionmember that is supported on the headrest frame, the dynamic damper beingembedded in the cushion member so that when viewed from a side, theweight is present on an extension axis of the support tube.
 2. Thevehicle seat device according to claim 1, wherein the vibration systemfurther comprises a frame, and the dynamic damper is disposed so thatpart of the cushion member is present between the elastic member and theframe of the vibration system.
 3. The vehicle seat device according toclaim 2, wherein the dynamic damper is embedded in the cushion member ofthe headrest so that the center of gravity of the weight of the dynamicdamper is present above a center in an up-and-down direction of theheadrest.
 4. A vehicle seat device comprising a seat cushion disposed ona floor of a vehicle, a seat back linked to a rear end part of the seatcushion, and a headrest fitted to an upper end part of the seat back,the seat back and the headrest cooperating to form a vibration systemequipped with a dynamic damper, wherein: the dynamic damper comprises anelastic member that is embedded within a cushion member of the vibrationsystem, and a weight embedded in the elastic member, the weight has acenter of gravity which is offset upwardly or downwardly from a centerof the cushion member, the weight has an asymmetric shape in at leastone of a lateral direction and an up-and-down direction, the headrestcomprises a headrest frame and the cushion member, the headrest frame isformed from a frame lower portion supported on the support tube so thatthe frame lower portion can move up and down and be fixed, the supporttube being fixedly provided on an upper end part of a seat back frame ofthe seat back, and a frame upper portion bending forward from an upperend of the frame lower portion and extending obliquely upward, thecushion member is supported on the frame upper portion, and the dynamicdamper is embedded in the cushion member so as to be positioned to therear of the frame upper portion.
 5. A vehicle seat device comprising aseat cushion disposed on a floor of a vehicle, a seat back linked to arear end part of the seat cushion, and a headrest fitted to an upper endpart of the seat back, the seat back and the headrest cooperating toform a vibration system equipped with a dynamic damper, wherein: thedynamic damper comprises an elastic member that is embedded within acushion member of the vibration system, and a weight embedded in theelastic member, the weight has a center of gravity which is offsetupwardly or downwardly from a center of the cushion member, the weighthas an asymmetric shape in at least one of a lateral direction and anup-and-down direction, and the dynamic damper is embedded as a pair inleft and right shoulder parts of the cushion member of the seat back. 6.The vehicle seat device according to claim 1, wherein the weight of thedynamic damper is formed so that an upper half portion of the weight hasa mass that is larger than a mass of a lower half portion.
 7. Thevehicle seat device according to claim 2, wherein the weight of thedynamic damper is formed so that an upper half portion of the weight hasa mass that is larger than a mass of a lower half portion.
 8. Thevehicle seat device according to claim 3, wherein the weight of thedynamic damper is formed so that an upper half portion of the weight hasa mass that is larger than a mass of a lower half portion.
 9. A vehicleseat device comprising a seat cushion disposed on a floor of a vehicle,a seat back linked to a rear end part of the seat cushion, and aheadrest fitted to an upper end part of the seat back, the seat back andthe headrest cooperating to form a vibration system equipped with adynamic damper, wherein: the dynamic damper comprises an elastic memberthat is embedded within a cushion member of the vibration system, and aweight embedded in the elastic member, the weight has a center ofgravity which is offset upwardly or downwardly from a center of thecushion member, the weight has an asymmetric shape in at least one of alateral direction and an up-and-down direction, and the elastic memberof the dynamic damper is formed so that a spring constant thereof variesbetween that when the weight vibrates in a fore-and-aft direction of thevehicle and that when the weight vibrates in a left-and-right directionof the vehicle.